With the development of communication technology, the standard of wireless communication system has the characteristics of high data rate, large user capacity and low power consumption. As a key component of front-end, power amplifier has a great influence on transmitter performance. Therefore, the power amplifier with high efficiency and broadband operation has made considerable progress.
To improve efficiency, a variety of switch mode PAs are proposed, such as Class-D, Class-E and Class-F PAs. Theoretically, the efficiency of the above power amplifier can reach 100%. Doherty and envelope tracking structure are used to improve efficiency and linearity. To maintain bandwidth efficiency and maintain high efficiency, various technologies have been put forward. On the basis of standard switch mode PAs, continuous Class-B/J, continuous Class-F and continuous Class-F−1, are proposed, which alleviate the requirement on terminating impedance of harmonics from fixed values into purely reactive regions and thus achieve satisfactory bandwidth. After that, extended continuous mode PA further relaxes the requirements of harmonic impedances to reactive-resistive ones with a small degradation in efficiency.
Power amplifiers are usually cascaded with low insertion loss bandpass filters to suppress the out-of-band interference. Although the bandwidth of the continuous power amplifier has reached one octave, the overall bandwidth and efficiency are degraded due to the interconnection mismatching and insertion loss of the filter. In order to overcome this problem, the co-design of power amplifier and bandpass filter has been studied widely. They mainly focus on miniaturization, power efficiency enhancement (PAE) and selectivity improvement.
However, the preceding filtering PA designs have high selectivity and overall PAE, while the bandwidth with large PAE is relatively small due to the limited design freedom.